This invention relates to an improvement in the process for production of titanium dioxide using the sulfuric acid digestion method by reacting ilmenite and/or titanium-containing slags with highly concentrated sulfuric acid, dissolving the solid reaction product with water and/or aqueous sulfuric acid, and separating the insoluble raw material fraction to obtain a sulfuric-acid-containing titanylsulfate solution rich in foreign metal salts (hereinafter referred to as the "black solution").
In optional steps, trivalent iron can be reduced and after crystallization of iron sulfate heptahydrate, that material can be separated. Thereupon, the black solution is subjected to hydrolysis, with subsequent separation of the titanium oxide hydrate which is precipitated, intensive washing with water, drying and, optionally, calcination.